Probes and similar devices are often employed, especially within the oil, gas and process industry, among other things in order to monitor any corrosion in the internal system. For example, this may be corrosion probes or weightloss coupons which are screwed into process tubing, into well heads, into water injection systems, etc. By using a small threaded nipple or recess fitting with internal threads and a sealing system, a probe may be positioned within the pipe, putting it in direct contact with the process medium.
When it comes to corrosion of probes as well as weightloss coupons, these items must be replaced relatively often. This may, for example, be due to the variable and short working life of probes and planned inspections in connection with weightloss coupons.
In order to carry out such replacements, the traditional method has been the application of mechanical tools, such as so-called retrievers. This involves a ball valve which may be threaded directly onto the nipple into which the probe is threaded. Further, a mechanical retriever is connected, which comprises a double cylinder and an internal, axially movable and rotable rod which makes it possible to move a threaded plug with a probe into or out of the nipple.
A significant disadvantage with the traditional mechanical system is that the cylinder with the rod is very long, ordinarily between 1.8 and 2.0 meters. This sets significant limitations on practical usage, insofar as use with nipples which are located near other pipes or close to decks, floors or ceilings. Often these items cannot be serviced due to lack of space. The movable cylinder with the connecting rod can also represent an element of risk, since quick, axial displacement which may occur as the result of lack of pressure blancing in the retriever may cause injury to the operator. The relatively heavy weight of these devices also represents a disadvantage, inasmuch as both transportation as well as operation of the tool is physically difficult.
A device is shown in U.S. Pat. No. 4,916,797 which in a large degree solves the problems connected to known mechanical retrievers. In this publication, a device is shown which does not require the use of an internal rod with the mechanical transfer of the rod in or out of the nipple. Instead, the plug is fastened into the nipple which makes rotation of the device unnecessary. Further, the plug and probe are constructed with sealing rings so that by taking advantage of the hydraulic pressure differences, the probe and plug may be pushed into or out of the nipple.
However, the hydraulic retriever which is disclosed in U.S. Pat. No. 4,916,797 may only be employed upon the availability of excess pressure in the pipe or tank. Further, the probe may jam in some instances, so that the excess pressure in the pipe is not high enough to be able to allow it to be removed. In such cases, mechanical retrievers must be used. Then, the disadvantage arises where one may employ the familiar hydraulic retriever in those cases in which access is difficult, but additionally there must be made available a mechanic retriever for those places where there is a vacuum, low pressure, no pressure difference or a low excess pressure in the pipe or tank.